In motorcycles having water cooled engines, the space for accommodation of a radiator is rather limited, for reasons not only of dimensions, but also of cooling capacity, external appearance, and other considerations. Generally, the radiator is positioned between the front fork supporting the front wheel and the power unit of the engine supported by the motorcycle frame, and is fixed to the upper portion of the latter. The radiator normally comprises a core between two tanks for coolant inflow and coolant outflow, respectively. Within the core there are a number of tubes extending in various directions, forming a coolant circuit connecting the tanks, and fins to expand the cooling surface area are arranged between these tubes. Hoses connect the tanks to the coolant inlet and outlet of the engine, respectively. The radiator has a generally square cross section, and is somewhat wider than it is high. In order to increase the heat release effect, the heat release surface area is made as large as possible, and for reasons of appearance, especially in the case of motorcycles, the device preferably has a vertically elongated shape.
However, particularly in the case of V-type engine motorcycles, because the upper portion of the engine protrudes in front of the frame, the area between the front fork and the engine (i.e., the space between the front fender and the radiator) is narrow. Thus, if a vertically elongated box type radiator is used, the expansion and contraction strokes of the front fork cannot be properly accommodated. For this reason, when this type of radiator is to be used, the space between the front fork and the engine must be expanded, and a motorcycle with a V-type engine cannot be scaled down to a smaller size. On the other hand, if the expansion of this space is to be avoided, it then becomes necessary to obtain the required heat release surface area by designing the radiator in a horizontally elongated form. The result of this expedient is to sacrifice the external appearance of the motorcycle, making it impossible to produce a motorcycle having a body which is slim and of narrow width.